The behaviour of second phase particles in molten steel processing vessels was investigated, using the E.S.Z. (Electric Sensing Zone) method, in conjunction with aqueous modelling and molten steel systems. / 1. Slag droplet entrainment/dispersion is an axisymmetric gas injection stirred system was investigated: A tank containing a water-olive oil simulation of stirred ladles of molten steel was used. Extensive numerical predictions of the oil (slag) droplet population distributions within the vessel were also carried out, and reasonable agreement with the experimental data achieved. Droplet dispersions were shown to be time and spatially dependent. / 2. Inclusion separation characteristics in tundishes of continuous steel casting operations were investigated. The mixed reactor model proved to be adequate for predicting particle separation behaviour, proved that the effective upper surface area of the dispersed plug flow region is known, a priori. / 3. An on-line method for the detection and measurement of inclusions in molten steel systems was developed. Inclusion removal rates within an induction furnace, as well as inclusion separation behaviour in a commercial scale tundish for continuous billet casting, were measured.

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The effect of increasing hot deformation on inclusion parameters such as area fraction (AF), the average inclusion length (Co), the inter-inclusion distance (D), the aspect ratio (FF) and the density of distributions (N);bas been quantitatively analysed by use of Quantimet 720, an image analysing computer and direct microstructural measurements. Two types of X-70 pipeline steel, one a semi-killed conventional (CON) steel, the other a fully killed and calcium treated for inclusion shape control (CAT) steel were examined in this research. Four stages of hot reduction of the CON steel viz. S2 (38% reduced), S3 (70% reduced), S4 (88% reduced) and S6 (97% reduced) and two stages of the CAT steel viz. CI (63% reduced) and C2 (95% reduced) were used in the investigation. The effect of inclusion parameters on the yield strength, total ductility and elastic and elastic-plastic fracture toughness of these materials were investigated to establish the role of inclusions in the ductile, ductile-brittle transition and brittle fracture processes. The elastic and elastic-plastic fracture toughness of the specimens were measured by KJC testing as per ASTM standard E-399-78a method and unloading compliance J-integral technique as per ASTM standard respectively. It was observed that the semi-killed CON steel containing elongated inclusions shows anisotropy in elastic-plastic fracture toughness; whereas the CAT steels with globular inclusions exhibited isotropic elastic-plastic fracture toughness. The inclusion parameters shape, size and distribution do not affect the yield strength of the X-70 steel. The inclusion parameters markedly affect the elastic-plastic fracture toughness properties of the X-70 CON steel, particularly in the ductile and transition temperature region where failure occurs by the mechanism of microvoid coalescence. The effect of inclusions on the elastic fracture toughness in the brittle temperature region, where fracture occurs by cleavage mechanism, is insignificant. The most significent inclusion parameters which affect the elastic-plastic fracture toughness in the ductile fracture regime are the area fraction AF and the inter-inclusion spacing (D). The elastic-plastic fracture toughness of the CON and CAT X-70 pipeline steel at RT has been correlated (i) with AF by the following relation: [figure 1]. (ii) with D by the following relation: [figure 2]. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Extensive computer predictions have been carried out by the author to study flow, addition dispersion and particle motion during central gas injection into cylindrical vessels. In conjunction with numerical computations, experiments were conducted in a 0.30 scale water model of a 150 ton steel processing ladle, using a Froude number scaling criterion. Two typical gas injection configurations (i.e., conventional central injection and C.A.S. alloy addition procedure) were investigated. / Flow visualization studies were carried out using a suspended network of silken threads, mean velocity vectors and overall flow patterns were determined by video recording techniques, while mean velocity vectors and associated turbulence level were also measured with laser doppler velocimetry. These measurements show very reasonable agreement with equivalent numerical predictions. / To simulate the subsurface motion of additions, spherical wooden balls of various densities were dropped from typical heights, and their subsurface trajectories, immersion times, etc., recorded by means of a video recorder. Frame by frame analysis of the video tapes showed trends which are in good accord with computed trajectories. / Mixing times of simulated molten additions were measured by the conductivity measurement technique. These were compared with prediction from an equivalent tracer dispersion model and excellent agreement achieved. / For industrial application, flow, particle motion, and mixing times in a 150 ton steel processing ladle have been predicted and their technological significance discussed.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / M.S.